|-440||Greece||Democritus and Leucippus hypothesize that matter is composed of atoms.|
|750||Arab World||Jabir ibn Hayyan prepares acetic acid, the first pure acid.|
|900||Arab World||First production of concentrated alcohol, by distilling wine.|
|1300||Germany||False Geber describes the preparation of sulphuric acid.|
|1597||Germany||Libavius' Alchemia is the first chemistry textbook, with detailed descriptions of many chemical methods.|
|1624||Belgium||Jan van Helmont recognizes that more than one air-like substance exists and coins the term gas to describe any compressible fluid.|
|1661||England||Robert Boyle's Skeptical Chymist separates chemistry from medicine and alchemy; defines elements and chemical analysys.|
|1662||England||Robert Boyle states Boyle's Law, that the volume occupied by a fixed mass of gas in a container is inversely proportional to the pressure it exerts.|
|1674||Germany||Hennig Brand discovers phosphorus, a.n. 15, the first element known to have been discovered by a specific person, and the first element not known in any earlier form.|
|1735||Sweden||Georg Brandt discovers cobalt, a.n. 27, the first discovery of a metal not known to the ancients.|
|1751||Sweden||Axel Cronstedt discovers nickel, a.n. 28, the first metal since iron found to be subject to magnetic attraction.|
|1755||Scotland||Joseph Black identifies "fixed air" (carbon dioxide), the first application of quantitative analysis to chemical reactions.|
|1766||England||Henry Cavendish discovers "inflammable air" (hydrogen, a.n. 1).|
|1772||France||Antoine Lavoisier discovers that air is absorbed during combustion, and that diamond consists of carbon.|
|Daniel Rutherford, Carl Scheele, Joseph Priestley, and Henry Cavendish independently discover "mephitic air" (nitrogen, a.n. 7).|
|Joseph Priestley and Carl Scheele independently discover "respirable air" (oxygen, a.n. 8).|
|1774-1925||The discovery of the rest of naturally occuring elements becomes a central quest of chemists for the next century and a half. Most of these discoveries qualify as central events, but only the elements of special significance are included here.|
|1775||France||Antoine Lavoisier accurately describes combustion, discrediting phlogiston theory.|
|1779||France||Antoine Lavoisier discovers that the gas identified by Joseph Priestley and Carl Scheele is responsible for combustion. He names it oxygen.|
|1784||England||Henry Cavendish discovers the chemical composition of water.|
|1785||France||Claude Berthollet determines the composition of ammonia.|
|1789||France||Antoine Lavoisier's Traité Élémentaire de Chemie, a founding document in quantitative chemistry, states the law of conservation of matter.
||1797||France||Joseph Proust proposes his law of definite proportions, followed by experimental evidence obtained in 1799.
||1800||England||William Nicholson and Anthony Carlisle discover that an electric current can bring about a chemical reaction (electrolysis), founding electro-chemistry.
||1801||France||Rene Haüy's four-volume Traité de Minéralogie founds crystallography.
||1803||England||John Dalton publishes the modern statement of atomic theory and introduces that concept of atomic weight.
||1803||France||Claude Berthollet's Essai de Statique Chemique lays the foundation for understanding chemical reactions and is a step toward the law of mass action.
|Fredrich Sertürner isolates morphine from laudanum, initiating the study of alkaloids.
||1806||France||Louis Vauquelin isolates asparagine, first of the amino acids.
||1811||Italy||Amadeo Avogadro hypothesizes that all gases at the same volume, pressure, and temperature are made up of the same number of particles.
||1813||Sweden||Jöns Berzelius develops the foundation of universal chemical notation.
||1814||Germany||Joseph von Fraunhofer discovers that the relative positions of spectral lines is constant, forming the basis for modern spectroscopy.
||1815||France||Joseph Gay-Lussac identifies the first organic radical (cyanogen, the cyano group).
||1817||France||Joseph Caventou and Pierre Pelletier isolate chlorophyll.
||1820||Germany||Joseph von Fraunhofer invents the diffraction grating for studying spectra.
||1823||England||Michael Faraday produces the first laboratory temperatures below 0oF, enabling liquefication of gases, a founding event in cryogenics.
||1825||England||Michael Faraday discovers and isolates benzene.
||1828||Germany||Friedrich Wöhler prepares the organic compound urea from inorganic compounds, the first synthesis of an organic substance, founding organic chemistry.
||1831||Scotland||Thomas Graham discovers Graham's Law, that the ratio of the speeds at which two different gases diffuse is inverse to the ratio of the square roots of the gas densities, a founding event in physical chemistry.
||1836||Germany||Theodore Schwann isolates pepsin, the first animal enzyme.
||1836||Sweden||Jöns Berzelius discovers a common force among catalytic reactions and introduces the terms catalysis and catalytic force.
||1840||Germany||Christian Schönbein discovers ozone.
||1846||France||Louis Pasteur discovers crystal asymmetry.
||1852||England||Edward Frankland describes the phenomenon that later became known as valence.
||1858||Germany||Friedrich Kekulé establishes two major facts of organic chemistry: carbon has a valence of four and carbon atoms can chemically combine with one another.
|Archibald Couper and Friedrich Kekulé develop a system for showing organic molecular structure graphically.
||1859||Germany||Gustav Kirchhoff and Robert Bunsen discover that each element is associated with characteristic spectral lines.
|James Maxwell develops the first extensive mathematical kinetic theory of gases, later augmented in collaboration with Ludwig Boltzmann.
||1860||Italy||Stanislao Cannizzaro introduces a reliable method of calculating atomic weights, leading to acceptance of Avogadro's Hypothesis and opening the way to classification of the elements.
||1863||England||John Newland's Law of Octaves stimulates work on the table of elements.
||1863||Norway||Cato Guldberg and Peter Waage discover the law of mass action, regarding the relationship of speed, heat, and concentration in chemical reactions.
||1865||Germany||Friedrich Kekulé discovers the structure of the benzene ring, enabling the solution of many problems of molecular structure.
|Pierre Janssen and Joseph Lockyer discover helium, a.n. 2, based on spectral analysis rather than a physical specimen.
||1869||Ireland||Thomas Andrews identifies the critical temperature for liquifying gases.
||1869||Russia||Dimitri Mendeleyev publishes a periodic table of the elements, including the prediction of undiscovered elements.
||1873||Netherlands||Johannes van der Waals provides a molecular explanation for the critical temperature above which gas can exist only as a gas.
|Jacobus Van't Hoff and Joseph Le Bel independently discover that the four bonding directions of the carbon atom point to the four vertices of a regular tetrahedron, founding stereochemistry.
|Louis Cailletet and Raoul Pictet independently liquefy oxygen, nitrogen, and carbon dioxide, the first liquefaction of gases.
|Ira Remsen and Constantin Fahlberg synthesize saccharin.
||1884||Germany||Emil Fischer discovers purines, which turn out to be an important part of nucleic acids, which in turn prove to be the key molecules of living tissues.
||1884||Sweden||Svante Arrhenius introduces the theory of ionic dissociation.
||1885||Switzerland||Johann Balmer develops a formula for the wavelengths at which hydrogen atoms radiate light.
||1886||France||Ferdinand Moissan isolates fluorine, a.n. 9, after 75 years of effort by others.
|William Ramsay and Per Teodor Cleve independently discover helium on earth.
||1898||Scotland||James Dewar invents a method of producing liquid hydrogen in quantity.
||1901||USA||Jokichi Takamine and John Abel independently isolate adrenaline, the first pure hormone.
||1904||England||Frederic Kipping discovers silicones.
||1905||Germany||Richard Willstätter discovers the structure of chlorophyll.
||1906||Russia||Mikhail Tsvet invents chromatography for studying dyes, eventually applied to complex chemical mixtures generally.
||1926||USA||James Sumner prepares the first crystallized enzyme, urease.
|Clinton Davisson and George Thomson independently create large nickel crystals that exhibit X-ray diffraction, confirming Louis de Broglie's theory of matter waves.
||1931||USA||Harold Urey discovers deuterium, heavy hydrogen.
|Walter Haworth and Tadeus Reichstein synthesize vitamin C.
||1934||France||Irène and Frédéric Joliot-Curie develop the first artificial isotope, a radioactive form of phosphporus.
|Emilio Segrè and Carlo Perrier prepare technetium, a.n. 43, the first artificial element.
||1938||Switzerland||Albert Hofmann and Arthur Stoll synthesize LSD, later (1943) recognized as a hallucinogen.
||1944||England||Archer Martin and Richard Synge invent paper chromatography, a faster form of chromatography that requires only a few drops of the substance being analyzed.
||1949||Derek Barton describes the conformation of a steroidal molecule having several six-membered carbon rings, changing the way organic chemists view molecules.